Hand-held injection devices are widely used for the self-injection of liquid drugs in a number of therapies. They are, for example, commonly used for the self-injection of liquid insulin formulations by diabetics, for the injection of growth hormones and a variety of further therapies. In the following, reference is mainly made to the self-injection of liquid insulin formulations as an exemplary field of application. Devices, methods, and kits in accordance with the present disclosure are therefore generally designed to be applied in diabetes therapy, without excluding further applications. Injection devices in accordance with the present disclosure are designed to administer the total volume of drug that is held by a drug reservoir in a number of single injections over an extended time period of typically several days up to several weeks.
In the context of the present disclose, the phrase “injection device” refers to a device that is designed for carrying out injections, an injection including the steps of temporarily fluidically coupling the injection device to a person's tissue, typically the subcutaneous tissue. An injection further includes administering an amount of liquid drug into the tissue and decoupling or removing the injection device from the tissue. In the context of the present disclosure, “Injection” should be distinguished from “infusion”. An infusion device is permanently coupled to the tissue for an extended time period and virtually permanently, night and day, in some cases, for example in diabetes therapy by Continuous Subcutaneous Insulin Infusion.
For an injection of liquid insulin formulations, hand-held injection devices of the pen-type are commonly used. Those pen-type injection devices include, in an operable state, a typically cylindrical drug cartridge which holds a volume of typically between 1 ml and 3 ml of a liquid insulin formulation. The drug cartridge may be either replaceable by a device user or be readily built-in, resulting in the whole injection device being disposable. The injection device further includes an injection cannula for the subcutaneous injection or a coupler for such cannulas. Those pen-type injection devices further include a drive unit with a threaded spindle for controlled displacement of a plunger inside the drug cartridge, thus forcing defined drug volumes out of the cartridge and into the cannula. The drive unit further includes a dose setting control, typically in form of a dose setting knob with a scale, wherein manual rotation of the dose setting knob sets a desired drug volume to be injected. The drive unit further includes a typically manually actuated injection actuator which is operated by the user for actually carrying out an injection. Typically, the injection actuator is integral with the dose setting knob, wherein the dose setting knob is pressed down, e.g. using a thumb, for carrying out the injection.
For most devices, the injection cannula, the drug cartridge and the drive unit, in particular the spindle, are arranged in-line, having a common longitudinal axis. This type of arrangement results in a pen-like shape, having a length of typically 10 cm to 20 cm and a typically circular or near-circular cross section of 1 cm to 3 cm in diameter. For carrying out an injection, the user first sets the dose to be injected, typically with one hand holding the device and the other hand operating the dose setting knob. For carrying out the injection, the device is held in a fist, the cannula is inserted into the tissue, e.g. of an arm or leg, followed by the thumb of the holding hand pressing down the dose setting knob.
In some devices, the drive unit includes an electrical drive unit, typically including a rotary motor with gearbox and corresponding control circuitry, rather than a manually operated drive. Those devices are somewhat more convenient and may offer additional functionality, such as automatic logging of injections, including download to a standard Personal Computer (PC or the like). The general way of operation, however, is identical.